Because of the growth of Internet, the wideband access condition is getting mature now. Accordingly, it is believed that a large amount of wideband requirement at the access terminal will promote the core network to be brought in the DWDM system so as to increase the bandwidth capacity. Therefore, it is a tendency that the metro DWDM system will gradually be developed from a point-to-point framework to an encircled or a network framework. And, OADM is a key apparatus in the DWDM system. The OADM can integrate traditional SDH/SONET signals into a multi-channel WDM/SONET network so as to save the upgrade cost of the network apparatus.
Generally, OADM can be separated into two types: FOADM (Fixed OADM) and ROADM (Reconfigurable OADM). FOADM is the main stream in the market and can provide an upload and download function of the fixed wavelength. However, because it only provides the upload and download function for specific wavelengths, it is insufficient for the flexible demand of the metro core network. Therefore, in the metro core network, the function of FOADM will gradually be replaced by ROADM which can flexibly adjust the wavelength, and then gradually, FOADM will be used more frequently in the metro edge network and the access network. Moreover, FOADM can be further separated into TFF (Thin Film Filter) type, FBG (Fiber Bragg Grating) type and AWG (Array WaveGuide) type while being separated according to the adopting key component thereof. Because of the product characteristics of FOADM described above, FOADM will become cheaper and cheaper, and obviously, the price thereof will therefore become an important factor to change the purchase desire of the clients. On the other hand, ROADM can be separated into a switch-based OADM and a tunable filter-based OADM, and the price thereof is quite expensive.
Because the Bragg grating will be utilized in the present invention, an introduction of the grating is presented here. For FBG-based OADM, basically, the construction thereof is to set plural FBGs between two circulators. And, these FBGs will respectively reflect specific uplink/downlink wavelength signals and be passed by thru wavelength signals. However, in FBG-based OADM, it is still hard to avoid a loss as the signal is passed through the uplink/downlink and the thru route. And, this type of OADM is easily changed by the temperature. Furthermore, because The FBG-based OADM also needs an amplifier for operating, the volume thereof must be bigger than others so that it will be difficult to be integrated with semiconductor wafers for reducing the cost.
On the other hand, because the wavelength value of the fiber grating is decided by the period between grating fringes written on the core, a reflection-wavelength tunable FBG can be obtained through appropriately adjusting that period. But, if that period is adjusted through altering the temperature, it will appear that the tunable range of wavelength is small and the adjusting speed is also slow, and thus this is unpractical for the industries.
Recently, because silicon can be obtained easily and the price thereof is also low, it already becomes the mainly used material in IC manufacturing. The present invention accordingly utilizes an SOI (silicon on insulator) as a wafer substrate. Regarding the SOI wafer, it is not only advantageous of easy obtainment and low price but also advantageous that the SOI structure can be integrated with advantageous characteristics of CMOS electronic devices, for example, high bandwidth and low power loss. Therefore, the present invention utilizes an SOI IC semiconductor manufacturing technique in manufacturing the critical component for fiber communication. And, it is believed that in the future, the SOI IC semiconductor manufacturing technique will be good at effectively reducing component size and promoting technical competitiveness.
Hence, the present invention employs the SOI for being designed into a tunable OADM (Optical Add/Drop Multiplexer) so as to form a wavelength selectable component, and further, the present invention also develops a protective network of an intelligent wavelength division multiplexing optical network for increasing the reliability of the intelligent wavelength division multiplexing optical network. Moreover, through utilizing the characteristics of multimode interference, the power transmission and coupling efficiency of the component can be significantly increased in the present invention so as to improve the output quality and increase the fiber coupling efficiency. Furthermore, in the design of the present invention, because it only needs to alter the parameters of the waveguide for outputting wavelengths at different sections, this can be applied to all wavelengths for all kinds of technical applications. Consequently, the design according to the present invention is advantageous of effectively saving at least half the area of the wafer and having a small and fine size, high procedure parameter variation tolerance, stable output, and low power loss etc. Accordingly, the present invention is an excellent solution for commercializing the future component.
Recently, there have already some documents regarding the integrated optical component which utilizes SOI as a manufacturing wafer.
In IEEE Photonics Technology Letters, vol. 13, No. 6, pp. 582-584, Rodney C. Tucker and Richard Lauder propose three new OADM architectures with low crosstalk and low component count. These OADMs are composed of a single multiport optical circulator and one or more fiber Bragg grating and have been experimentally proved to tolerate a large power difference.
According to Journal of Lightwave Technology, vol. 19, No. 9, pp. 1282-1286, David Mechin, Philippe Grosso, and Dominique Bosc, a photo-writing process of the Bragg grating and the lowering of the waveguide internal stresses are disclosed so as to increase the efficiency of Directional coupler (DC)-DADM and avoid the use of expensive optical circulators.
In Electronics Letters vol. 35, No. 15, pp. 1248-1249, Shih-Hsiang Hsu, O. King, F. G Johnson, J. V. Hryniewicz, Y. J. Chen and D. R. Stone design a wavelength division multiplexer through utilizing an optical detector array and a periodic grating. The optical detector is made of InGaAs, and the periodic waveguide grating has an AlGaAs/GaAs structure. The passband of a filter thereof is designed at 2 nm, and the wavelength thereof is ranged from 1520 to 1550 nm. However, the volume of the structure is big and the procedure thereof is also complicated.
In U.S. Pat. No. 5,875,272 “Wavelength Selective Optical Device” issued on Feb. 23, 1999, Anthony S. Kewitsch, George A. Rakuljic, Santa Monica and San Marino propose an add/drop filter which is composed of a mode coupler and a grating. This filter utilizes a bi-directional control and the length and the period of the grating for filtering a required wavelength, and the required wavelength can be feedback to the network so that the output and the next input will have an identical wavelength. However, a high manufacture quality of the grating which is not easy to be achieved is needed in this patent.
In U.S. Pat. No. 5,953,467 “Switchable Optical Filter” issued on Sep. 14, 1999, Christi Kay Madsen designs an optical filter comprising a Mach-Zehnder interferometer comprising a pair of optical waveguide arms extending between a pair of directional couplers. And, this pair of arms includes an alternating sequence of a phase shifter on at least one arm and a pair of reflective filters on each arm. Therefore, the filter is particularly useful as a gain equalization filter, an ADM filter and in an optical cross connection.
In U.S. Pat. No. 6,047,096 “Optical Device” issued on Apr. 4, 2000, Torsten Angustsson proposes a MMI-based (multimode interference-based) Bragg grating waveguide structure. In this structure, the Bragg grating is added into the multimode interference region for filtering so that the filtered wavelength can be received at other output ports. However, the grating still needs to be fabricated in this structure, and thus obviously, it will be more complicated.
According to Lauay Eldada, Randolph and Robert A. Norwood, U.S. Pat. No. 6,438,293 “Tunable Optical Add/Drop Multiplexer” issued on Aug. 20, 2002, it can be known that the core layer of the optical signal component includes a grating and a material, and through tuning the refractive index of the material, the grating will reflect a preselected wavelength of light. A single optical signal device can therefore be used to select a variety of wavelengths for segregation.
As described above, the four patents all utilize a waveguide component to serve as the coupler, filter and optical add/drop multiplexer for the division multiplexing, and it is thus evident that the optical add/drop multiplexer is an important component in the optical communication system and there is the necessity to develop a simpler and more convenient optical add/drop multiplexer.
Accordingly, the present invention utilizes a voltage variation to alter the dopant concentration, through which the refractive index can be changed, and thereby a specific signal can be dropped from the waveguide so as to control the router path of the specific wavelength signal.